Lightning strokes that are produced in electrical storms are the number one environmental cause of electric utility power interruptions across the United States. It is predicted that utility companies experience in excess of sixty percent of all their transmission system disturbances as a result of lightning events. Such lightning events also cause a majority of the damage that befalls a utility company's transmission system, which includes the thousands of miles of transmission lines that it owns, operates and maintains, and transmission line assets such as insulators, towers, etc. It is estimated that the damaging forces of lightning causes over one billion dollars in damage to homes, businesses, and forests, but most substantially, to electric power utilities.
Utilities have always been faced with the difficult task of maintaining their transmission system. The task is difficult because a transmission system covers a large amount of geographic territory, and the maintenance thereof must be performed in a limited amount of time with limited resources. Typically, utility companies maintain their transmission system assets by field inspectors who perform asset inspections out in the field. The inspection consists of performing a visual review of the assets to determine the assets' physical condition. For example, a large portion of a utility company's transmission lines are supported by miles of wood pole structures. Inspection of such wood pole structures are performed to assess whether the poles are damaged and whether the condition is likely to cause failures or disturbances.
Notwithstanding a utility company's efforts to perform physical inspection of its assets, a utility company cannot fully determine the performance characteristics (how the electrical parameters vary) of its transmission system assets based on field inspection data. Transmission system performance electrical characteristics are a much more difficult thing to assess. For example, it is not uncommon for the physical condition of a transmission system asset to appear to be in accordance with normal wear, when its performance condition is seriously deteriorated. This is a problem because the physical or visual appearance that the asset is normal when its electrical performance characteristics are poor may lead a utility company to believe that its assets can withstand lightning strokes of a certain magnitude and polarity when they cannot. When the performance characteristics of an asset are below normal, small lightning strokes may cause transmission system failure.
A common transmission system failure is an insulation flashover. Flashover involves poorly defined gas discharge physics, rapidly changing electromagnetic fields in which retardation plays a major role, nonlinear effects due to corona development on the conductors and on the tower itself, and frequency and current-dependent impedances on the earth. Insulation flashover may occur as a result of a number of factors, including: variations or increases in the tower footing resistance at each and/or every transmission system tower; a small puncture or deterioration of the transmission line insulators; or some subtle variation in some of those important electrical aspects. Flashover occurs when a lightning stroke hits a transmission line and either directly hits the energized conductor, or in many cases, indirectly hits the energized conductor by hitting some other portion of the structure, for example, the overhead shield wire. Such a direct or indirect strike by lightning causes the voltage to build up on that structure such that the voltage rise is large enough to cause the lightning to flashover the insulator to ground, thereby initiating a fault on the transmission line.
The problem with addressing flashover induced transmission system faults lies in the inability to address transmission system electrical weaknesses, which in most cases has a direct correlation to the electrical performance characteristics of the structure. Typically, assets that have electrical weaknesses also have electrical performance characteristics that are below normal. Addressing transmission system asset electrical weaknesses is a much more difficult task than assessing the mechanical and physical integrity of the asset. It is not an assessment task that can be performed by way of visual inspection.
It is possible for a utility company to discover poor performance characteristics through running diagnostic tests on its transmission system assets. However, to perform such tests would be difficult to implement and extremely expensive. There is a need for a method of determining performance characteristics without incurring the costs associated with diagnostic tests. There is also a need for a method of identifying deteriorated assets soon after the asset's performance characteristics fall below an acceptable level.
The need for a system that addresses the above described needs is further necessitated by the mandate of the Federal Energy Regulatory Commission (FERC) which requires the nation's electric utilities to open their private transmission systems to independent power companies. Independent power producers and competing producers will then use the electric utilities transmission system to move electricity from its source to their customers. The FERC is making these changes within the electric utilities industry to encourage competition for wholesale customers and perhaps eventually, retail customers. With the anticipated increased competition in the electric utilities industry resulting from the FERC's mandated open access, electric utility companies will be forced to increase the quality of their transmission systems and thereby the quality of electricity provided to customers. One of the ways in which quality will be increased is by reducing the number of disturbances and faults that occur on the electric utilities transmission system. Such quality increases will be necessary in order for utility companies to stay competitive in providing electric power to its customers, and because independent power producers and competing producers as customers using the utility company's transmission system will demand it.
A reduction in the number of disturbances or faults on an electric power utility transmission system has also become critical because the power quality requirements of electric power customers is substantially higher today than it used to be, and is constantly increasing. Advances in technology have and will continue to force customers to demand that electric utilities provide electrical power having increased consistency and fewer disturbances. By way of example, a larger number of customers are utilizing more sophisticated equipment that has higher voltage-sensitivity, such as computers and process control systems. Because lightning is in excess of sixty percent of all electric power transmission system disturbances, electric power utility companies are in need of a system and method that provides for a better understanding of the causal relationship between lightning and transmission system performance. With a better understanding of the causal relationship between lightning and utility transmission system performance, a utility company can take proactive steps in maintaining its transmission system, thereby reducing disturbances thereon.
Presently, the utility industry utilizes general purpose statistical modeling or simulation techniques to gain better understanding of the causal relationship between lightning and electric utility transmission system performance. The statistical modeling or simulation techniques used typically involve a computer simulation or modeling of the utility companies transmission system. Such models are typically of a digital simulation type wherein the transmission system assets and transmission lines are modeled to reflect performance in accordance with their defined characteristics. The model simulates the transmission system response to a plurality of different lightning engagement scenarios, wherein the lightning strokes are simulated at varying magnitudes and polarities. Analyzing the simulated transmission system's response to the plurality of different lightning conditions allows a utility company to make a hypothesis regarding how the actual transmission system lines and assets may perform in response to varying lightning events in the field. Such a hypothesis allows the utility company to make informed decisions concerning when utility assets may need to be replaced or repaired.
Although hypotheses regarding when utility assets may need to be replaced or repaired has proven useful, hypotheses generated from an electrical utility company's statistical modeling has significant drawbacks. The first draw back occurs because the structure of a transmission system stretches over a very large geographic area. As a result, hypotheses regarding the need for replacement or repair of a stretch of transmission line or assets on the transmission system is an expensive and difficult process. It is difficult because there are miles of transmission line and a large number of assets along the miles of transmission line with no way to pinpoint the exact location of the transmission system disturbance and thereby the section of the transmission line or the transmission system asset causing the disturbance. On the other hand, even if a transmission system disturbance could be located, the present simulation methods do not provide a means for determining whether the disturbance is a result of failing transmission system assets or a lightning event having a magnitude that causes a voltage on an asset that is greater than the voltage level capability of the asset.
Presently, there is no method of determining whether the transmission system assets that are at the root of lightning induced faults have performance problems that cause the fault. There is a need for a system and method whereby an electric power utility can perform an analysis on transmission system disturbances and faults to determine if the faults or disturbances are a result of the transmission assets not performing properly or whether the disturbance or fault occurs because the lightning event causes the voltage at the asset to exceed the threshold capability that the asset could withstand without a disturbance or fault. Such a system would eliminate replacement and repair of assets that are functioning properly but are involved in disturbances or faults caused by lightning events having a magnitude that causes the voltage level of the assets to exceed their threshold voltage capability.
Presently, in response to transmission system disturbances or faults, a utility company has no way of knowing or determining whether the disturbance or fault is a result of faulty transmission system assets, or whether the assets are performing properly and the lightning event magnitude causes the voltage level of the asset to exceed its threshold capability. Not knowing why faults and disturbances are occurring causes utility companies to make unnecessary replacement or repair of numerous assets in response to the disturbances or faults. Not knowing why fault and disturbances are occurring also causes delay of needed repairs as a larger statistically significant sample of events or faults are collected before a decision can be made to affect some change to an asset. Many of the assets replaced or repaired, including large sections of the transmission line, are typically performing in accordance within their appropriate specification levels. Such unnecessary replacement and repair results in substantial waste.
There is a need for a method and system that allows a utility company to more accurately pinpoint the location of faults and disturbances. There is also a need for a method or system that provides a means for analyzing the location of a fault or disturbance in order to determine whether the assets determined to have caused the fault or disturbance are functioning in accordance with their defined specification. The ability to more accurately pinpoint problem assets along a transmission system would result in substantial savings to a utility company. Such a system would eliminate premature replacement of assets and allow the utility company to utilize transmission assets for their full life.
The present invention provides a solution to the above needs and problems, and offers other advantages over the prior art.